Tesco's chief executive said the horsemeat scandal's impact on sales had been 'minimal'. Photograph: Andy Rain/EPA

Tesco has promised to buy more meat from the UK and install cameras at its suppliers' factories in an attempt to prevent another horsemeat-style scandal.

Phil Clarke, chief executive of the UK's biggest supermarket, where last month burgers containing up to 29% horsemeat were found, will tell the National Farmers Union (NFU) conference in Birmingham on Wednesday: "We are already the biggest customer of UK agriculture, with all our beef – fresh, frozen and in ready meals – coming from UK and Ireland farms. But we can do much more."

By July, all Tesco's fresh chicken will also come from British farms, with frozen and ready meals to be swapped over in future.

Clarke told Sky News on Wednesday morning: "We feel the need to bring the food closer to home. We think it's right to bring more of it back to the UK, so long as we can get the demand from the UK."

He insisted the impact on sales at the supermarket had been "minimal" but did admit that some customers were buying fewer frozen ready meals.

Clarke's promise to tighten up Tesco's supply chain shows growing concern among supermarkets about shoppers' loss of confidence in their processed food. Figures from Kantar Worldpanel out on Tuesday suggested that sales of frozen burgers in the UK had plunged 43% and frozen ready meals 13% since the emergence of the horsemeat scandal.

Clarke's comments came as the NFU president, Peter Kendall, used his opening address to the conference to call on supermarkets to source more from British farmers and growers. He said that, while supermarkets already bragged about sourcing certain meats, fresh fruit or dairy products in the UK, they needed to extend this activity to cheaper and processed foods.

"It's clear that the longer a supply chain and the more borders it crosses, the less traceable our food is and the more the chain is open to negligence at best, fraud and criminal activity at worst," Kendall said.

He added: "We now need the supermarkets to stop scouring the world for the cheapest products they can find and start sourcing high-quality, traceable product from farmers here at home."

Kendall said clearer country of origin labelling would help shoppers make informed choices, and he reserved particular criticism for Morrisons, the Bradford-based supermarket, which he said had recently relaxed its 100% buy-British policy on chicken to introduce the cheaper Hemsley range sourced outside the UK. Kendall suggested the English-sounding name range was a "disservice" to shoppers, 90% of whom want to buy British food according to a OnePoll survey commissioned by the union.